docs/users_guide/6.10.1-notes.xml

   1 <?xml version="1.0" encoding="iso-8859-1"?>
   2 <sect1 id="release-6-10-1">
   3   <title>Release notes for version 6.10.1</title>
   4
   5   <para>
   6     The significant changes to the various parts of the compiler are
   7     listed in the following sections.
   8   </para>
   9
  10   <sect2>
  11     <title>User-visible compiler changes</title>
  12     <itemizedlist>
  13       <listitem>
  14         <para>
  15           The new QuasiQuotes language extension adds
  16           general quasi-quotation, as described in
  17           "Nice to be Quoted: Quasiquoting for Haskell"
  18           (Geoffrey Mainland, Haskell Workshop 2007).
  19           See <xref linkend="th-quasiquotation" /> for more information.
  20         </para>
  21       </listitem>
  22       <listitem>
  23         <para>
  24           The new ViewPatterns language extension allows
  25           &quot;view patterns&quot;. The syntax for view patterns
  26           is <literal>expression -> pattern</literal> in a pattern.
  27           For more information, see <xref linkend="view-patterns" />.
  28         </para>
  29       </listitem>
  30       <listitem>
  31         <para>
  32           GHC already supported (e op) postfix operators, but this
  33           support was enabled by default. Now you need to use the
  34           PostfixOperators language extension if you want it.
  35           See <xref linkend="postfix-operators" /> for more information
  36           on postfix operators.
  37         </para>
  38       </listitem>
  39       <listitem>
  40         <para>
  41           The new TransformListComp language extension enables
  42           implements generalised list comprehensions, as described in
  43           the paper "Comprehensive comprehensions" (Peyton Jones &amp;
  44           Wadler, Haskell Workshop 2007).
  45           For more information see
  46           <xref linkend="generalised-list-comprehensions" />.
  47         </para>
  48       </listitem>
  49       <listitem>
  50         <para>
  51           If you want to use impredicative types then you now need to
  52           enable the ImpredicativeTypes language extension.
  53           See <xref linkend="impredicative-polymorphism" /> for more
  54           information.
  55         </para>
  56       </listitem>
  57       <listitem>
  58         <para>
  59           There is a new languages extension PackageImports which allows
  60           imports to be qualified with the package they should come
  61           from, e.g.
  62         </para>
  63 <programlisting>
  64 import "network" Network.Socket
  65 </programlisting>
  66         <para>
  67           See <xref linkend="package-imports" /> for more details.
  68         </para>
  69       </listitem>
  70       <listitem>
  71         <para>
  72           In earlier versions of GHC, the recompilation checker didn't
  73           notice changes in other packages meant that recompilation is
  74           needed. This is now handled properly, using MD5 checksums of
  75           the interface ABIs.
  76         </para>
  77       </listitem>
  78       <listitem>
  79         <para>
  80           When compiling with <literal>-fvia-C</literal>, we no longer
  81           use the C header files. Instead we rely on all the type
  82           information being given as part of the FFI import declaration.
  83           This makes it more consistent with <literal>-fasm</literal>.
  84         </para>
  85         <para>
  86           This means that, unlike <literal>-fasm</literal>,
  87           <literal>-fvia-C</literal> is no longer able to
  88           call varargs functions.
  89         </para>
  90         <para>
  91           Also, if you were using <literal>-fvia-C</literal> because
  92           your program didn't work with <literal>-fasm</literal>, then
  93           it probably won't work with <literal>-fvia-C</literal> either
  94           now.
  95         </para>
  96         <para>
  97           We recommend using <literal>-fasm</literal> (the default).
  98           We expect to remove the <literal>-fvia-C</literal>
  99           functionality in the 6.12 release.
 100         </para>
 101       </listitem>
 102       <listitem>
 103         <para>
 104           GHC now treats the Unicode "Letter, Other" class as lowercase
 105           letters. This is an arbitrary choice, but better than not
 106           allowing them in identifiers at all. This may be revisited
 107           by Haskell'.
 108         </para>
 109       </listitem>
 110       <listitem>
 111         <para>
 112           In addition to the <literal>DEPRECATED</literal> pragma, you
 113           can now attach arbitrary warnings to declarations with the new
 114           <literal>WARNING</literal> pragma. See
 115           <xref linkend="warning-deprecated-pragma" /> for more details.
 116         </para>
 117       </listitem>
 118       <listitem>
 119         <para>
 120           If GHC is failing due to <literal>-Werror</literal>, then it
 121           now emits a message telling you so.
 122         </para>
 123       </listitem>
 124       <listitem>
 125         <para>
 126           GHC now warns about unrecognised pragmas, as they are often
 127           caused by a typo. The
 128           <literal>-fwarn-unrecognised-pragmas</literal> controls
 129           whether this warning is emitted.
 130           The warning is enabled by default.
 131         </para>
 132       </listitem>
 133       <listitem>
 134         <para>
 135           There is a new flag
 136           <literal>-fwarn-dodgy-foreign-imports</literal> which controls
 137           a new warning about FFI delcarations of the form
 138         </para>
 139 <programlisting>
 140 foreign import "f" f :: FunPtr t
 141 </programlisting>
 142         <para>
 143           on the grounds that it is probably meant to be
 144         </para>
 145 <programlisting>
 146 foreign import "&amp;f" f :: FunPtr t
 147 </programlisting>
 148         <para>
 149           The warning is enabled by default.
 150         </para>
 151       </listitem>
 152       <listitem>
 153         <para>
 154           External core (output only) is working again.
 155         </para>
 156       </listitem>
 157       <listitem>
 158         <para>
 159           There is a new flag <literal>-dsuppress-uniques</literal> that
 160           makes GHC's intermediate core easier to read. This flag cannot
 161           be used when actually generating code.
 162         </para>
 163       </listitem>
 164       <listitem>
 165         <para>
 166           There is a new flag <literal>-dno-debug-output</literal> that
 167           suppresses all of the debug information when running a
 168           compiler built with the <literal>DEBUG</literal> option.
 169         </para>
 170       </listitem>
 171       <listitem>
 172         <para>
 173           A bug in earlier versions of GHC meant that sections didn't
 174           always need to be parenthesised, e.g.
 175           <literal>(+ 1, 2)</literal> was accepted. This has now been
 176           fixed.
 177         </para>
 178       </listitem>
 179       <listitem>
 180         <para>
 181           The <literal>-fspec-threshold</literal> flag has been replaced
 182           by <literal>-fspec-constr-threshold</literal> and
 183           <literal>-fliberate-case-threshold</literal> flags.
 184           The thresholds can be disabled by
 185           <literal>-fno-spec-constr-threshold</literal> and
 186           <literal>-fno-liberate-case-threshold</literal>.
 187         </para>
 188       </listitem>
 189       <listitem>
 190         <para>
 191           The new flag <literal>-fsimplifier-phases</literal>
 192           controls the number of simplifier phases run during
 193           optimisation. These are numbered from n to 1 (by default, n=2).
 194           Phase 0 is always run regardless of this flag.
 195         </para>
 196       </listitem>
 197       <listitem>
 198         <para>
 199           Simplifier phases can have an arbitrary number of tags
 200           assigned to them, and multiple phases can share the same tags.
 201           The tags can be used as arguments to the new flag
 202           <literal>-ddump-simpl-phases</literal>
 203           to specify which phases are to be dumped.
 204         </para>
 205
 206         <para>
 207           For example,
 208           <literal>-ddump-simpl-phases=main</literal> will dump the
 209           output of phases 2, 1 and 0 of the initial simplifier run
 210           (they all share the "main" tag) while
 211           <literal>-ddump-simpl-phases=main:0</literal>
 212           will dump only the output of phase 0 of that run.
 213         </para>
 214
 215         <para>
 216           At the moment, the supported tags are
 217           main (the main, staged simplifier run (before strictness)),
 218           post-worker-wrapper (after the w/w split),
 219           post-liberate-case  (after LiberateCase), and
 220           final (final clean-up run)
 221         </para>
 222
 223         <para>
 224           The names are somewhat arbitrary and will change in the future.
 225         </para>
 226       </listitem>
 227       <listitem>
 228         <para>
 229           The <literal>-fno-method-sharing</literal> flag is now
 230           dynamic (it used to be static).
 231         </para>
 232       </listitem>
 233     </itemizedlist>
 234   </sect2>
 235
 236   <sect2>
 237     <title>Deprecated flags</title>
 238
 239     <itemizedlist>
 240       <listitem>
 241         <para>
 242           The new flag <literal>-fwarn-deprecated-flags</literal>,
 243           controls whether we warn about deprecated flags and language
 244           extensions. The warning is on by default.
 245         </para>
 246       </listitem>
 247       <listitem>
 248         <para>
 249           The following language extensions are now marked as
 250           deprecated; expect them to be removed in a future release:
 251         </para>
 252         <itemizedlist>
 253           <listitem>
 254             <para>
 255               <literal>RecordPuns</literal>
 256               (use <literal>NamedFieldPuns</literal> instead)
 257             </para>
 258           </listitem>
 259           <listitem>
 260             <para>
 261               <literal>PatternSignatures</literal>
 262               (use <literal>ScopedTypeVariables</literal> instead)
 263             </para>
 264           </listitem>
 265         </itemizedlist>
 266       </listitem>
 267       <listitem>
 268         <para>
 269           The following flags are now marked as deprecated;
 270           expect them to be removed in a future release:
 271         </para>
 272         <itemizedlist>
 273           <listitem>
 274             <para>
 275               <literal>-Onot</literal>
 276               (use <literal>-O0</literal> instead)
 277             </para>
 278           </listitem>
 279           <listitem>
 280             <para>
 281               <literal>-Wnot</literal>
 282               (use <literal>-w</literal> instead)
 283             </para>
 284           </listitem>
 285           <listitem>
 286             <para>
 287               <literal>-frewrite-rules</literal>
 288               (use <literal>-fenable-rewrite-rules</literal> instead)
 289             </para>
 290           </listitem>
 291           <listitem>
 292             <para>
 293               <literal>-no-link</literal>
 294               (use <literal>-c</literal> instead)
 295             </para>
 296           </listitem>
 297           <listitem>
 298             <para>
 299               <literal>-recomp</literal>
 300               (use <literal>-fno-force-recomp</literal> instead)
 301             </para>
 302           </listitem>
 303           <listitem>
 304             <para>
 305               <literal>-no-recomp</literal>
 306               (use <literal>-fforce-recomp</literal> instead)
 307             </para>
 308           </listitem>
 309           <listitem>
 310             <para>
 311               <literal>-syslib</literal>
 312               (use <literal>-package</literal> instead)
 313             </para>
 314           </listitem>
 315           <listitem>
 316             <para>
 317               <literal>-fth</literal>
 318               (use the <literal>TemplateHaskell</literal> language
 319               extension instead)
 320             </para>
 321           </listitem>
 322           <listitem>
 323             <para>
 324               <literal>-ffi</literal>, <literal>-fffi</literal>
 325               (use the <literal>ForeignFunctionInterface</literal>
 326               extension instead)
 327             </para>
 328           </listitem>
 329           <listitem>
 330             <para>
 331               <literal>-farrows</literal>
 332               (use the <literal>Arrows</literal> language
 333               extension instead)
 334             </para>
 335           </listitem>
 336           <listitem>
 337             <para>
 338               <literal>-fgenerics</literal>
 339               (use the <literal>Generics</literal> language
 340               extension instead)
 341             </para>
 342           </listitem>
 343           <listitem>
 344             <para>
 345               <literal>-fno-implicit-prelude</literal>
 346               (use the <literal>NoImplicitPrelude</literal> language
 347               extension instead)
 348             </para>
 349           </listitem>
 350           <listitem>
 351             <para>
 352               <literal>-fbang-patterns</literal>
 353               (use the <literal>BangPatterns</literal> language
 354               extension instead)
 355             </para>
 356           </listitem>
 357           <listitem>
 358             <para>
 359               <literal>-fno-monomorphism-restriction</literal>
 360               (use the <literal>NoMonomorphismRestriction</literal> language
 361               extension instead)
 362             </para>
 363           </listitem>
 364           <listitem>
 365             <para>
 366               <literal>-fmono-pat-binds</literal>
 367               (use the <literal>MonoPatBinds</literal> language
 368               extension instead)
 369             </para>
 370           </listitem>
 371           <listitem>
 372             <para>
 373               <literal>-fextended-default-rules</literal>
 374               (use the <literal>ExtendedDefaultRules</literal> language
 375               extension instead)
 376             </para>
 377           </listitem>
 378           <listitem>
 379             <para>
 380               <literal>-fimplicit-params</literal>
 381               (use the <literal>ImplicitParams</literal> language
 382               extension instead)
 383             </para>
 384           </listitem>
 385           <listitem>
 386             <para>
 387               <literal>-fscoped-type-variables</literal>
 388               (use the <literal>ScopedTypeVariables</literal> language
 389               extension instead)
 390             </para>
 391           </listitem>
 392           <listitem>
 393             <para>
 394               <literal>-fparr</literal>
 395               (use the <literal>PArr</literal> language
 396               extension instead)
 397             </para>
 398           </listitem>
 399           <listitem>
 400             <para>
 401               <literal>-fallow-overlapping-instances</literal>
 402               (use the <literal>OverlappingInstances</literal> language
 403               extension instead)
 404             </para>
 405           </listitem>
 406           <listitem>
 407             <para>
 408               <literal>-fallow-undecidable-instances</literal>
 409               (use the <literal>UndecidableInstances</literal> language
 410               extension instead)
 411             </para>
 412           </listitem>
 413           <listitem>
 414             <para>
 415               <literal>-fallow-incoherent-instances</literal>
 416               (use the <literal>IncoherentInstances</literal> language
 417               extension instead)
 418             </para>
 419           </listitem>
 420           <listitem>
 421             <para>
 422               <literal>-optdep-s</literal>
 423               (use <literal>-dep-suffix</literal> instead)
 424             </para>
 425           </listitem>
 426           <listitem>
 427             <para>
 428               <literal>-optdep-f</literal>
 429               (use <literal>-dep-makefile</literal> instead)
 430             </para>
 431           </listitem>
 432           <listitem>
 433             <para>
 434               <literal>-optdep-w</literal>
 435               (has no effect)
 436             </para>
 437           </listitem>
 438           <listitem>
 439             <para>
 440               <literal>-optdep--include-prelude</literal>
 441               (use <literal>-include-pkg-deps</literal> instead)
 442             </para>
 443           </listitem>
 444           <listitem>
 445             <para>
 446               <literal>-optdep--include-pkg-deps</literal>
 447               (use <literal>-include-pkg-deps</literal> instead)
 448             </para>
 449           </listitem>
 450           <listitem>
 451             <para>
 452               <literal>-optdep--exclude-module</literal>
 453               (use <literal>-exclude-module</literal> instead)
 454             </para>
 455           </listitem>
 456           <listitem>
 457             <para>
 458               <literal>-optdep-x</literal>
 459               (use <literal>-exclude-module</literal> instead)
 460             </para>
 461           </listitem>
 462         </itemizedlist>
 463       </listitem>
 464       <listitem>
 465         <para>
 466           The following flags have been removed:
 467         </para>
 468         <itemizedlist>
 469           <listitem>
 470             <para>
 471               <literal>-no-link-chk</literal>
 472               (has been a no-op since at least 6.0)
 473             </para>
 474           </listitem>
 475           <listitem>
 476             <para>
 477               <literal>-fruntime-types</literal>
 478               (has not been used for years)
 479             </para>
 480           </listitem>
 481           <listitem>
 482             <para>
 483               <literal>-fhardwire-lib-paths</literal>
 484               (use <literal>-dynload sysdep</literal>)
 485             </para>
 486           </listitem>
 487         </itemizedlist>
 488       </listitem>
 489       <listitem>
 490         <para>
 491           The <literal>-unreg</literal> flag, which was used to build
 492           unregisterised code with a registerised compiler, has been
 493           removed. Now you need to build an unregisterised compiler
 494           if you want to build unregisterised code.
 495         </para>
 496       </listitem>
 497     </itemizedlist>
 498   </sect2>
 499
 500   <sect2>
 501     <title>GHC API changes</title>
 502
 503     <itemizedlist>
 504       <listitem>
 505         <para>
 506           There is now a Ghc Monad used to carry around GHC's
 507           Session data. This Monad also provides exception handling
 508           functions.
 509         </para>
 510       </listitem>
 511       <listitem>
 512         <para>
 513           It is now possible to get the raw characters corresponding to
 514           each token the lexer outputs, and thus to reconstruct the
 515           original file.
 516         </para>
 517       </listitem>
 518       <listitem>
 519         <para>
 520           GHCi implicitly brings all exposed modules into scope with
 521           qualified module names. There is a new flag
 522           <literal>-fimplicit-import-qualified</literal>
 523           that controls this behaviour, so other GHC API clients can
 524           specify whether or not they want it.
 525         </para>
 526       </listitem>
 527       <listitem>
 528         <para>
 529           There is now haddock documentation for much of the GHC API.
 530         </para>
 531       </listitem>
 532     </itemizedlist>
 533   </sect2>
 534
 535   <sect2>
 536     <title>GHCi changes</title>
 537
 538     <itemizedlist>
 539       <listitem>
 540         <para>
 541           You can now force GHCi to interpret a module, rather than
 542           loading its compiled code, by prepending a * character to its
 543           name, e.g.
 544         </para>
 545 <programlisting>
 546 Prelude> :load *A
 547 Compiling A                ( A.hs, interpreted )
 548 *A>
 549 </programlisting>
 550       </listitem>
 551       <listitem>
 552         <para>
 553           By default, GHCi will not print bind results, e.g.
 554         </para>
 555 <programlisting>
 556 Prelude&gt; c &lt;- return 'c'
 557 Prelude&gt;
 558 </programlisting>
 559         <para>
 560           does not print <literal>'c'</literal>. Use
 561           <literal>-fprint-bind-result</literal> if you want the old
 562           behaviour.
 563         </para>
 564       </listitem>
 565       <listitem>
 566         <para>
 567           GHCi now uses editline, rather than readline, for input.
 568           This shouldn't affect its behaviour.
 569         </para>
 570       </listitem>
 571       <listitem>
 572         <para>
 573           The GHCi prompt history is now saved in
 574           <literal>~/.ghc/ghci_history</literal>.
 575         </para>
 576       </listitem>
 577       <listitem>
 578         <para>
 579           GHCi can now use libffi to make FFI calls, which means that
 580           it now works on all platforms that libffi supports.
 581         </para>
 582       </listitem>
 583     </itemizedlist>
 584   </sect2>
 585
 586   <sect2>
 587     <title>Runtime system changes</title>
 588
 589     <itemizedlist>
 590       <listitem>
 591         <para>
 592           If the user presses control-C while running a Haskell program
 593           then the program gets an asynchronous UserInterrupt exception.
 594         </para>
 595       </listitem>
 596       <listitem>
 597         <para>
 598           We now ignore SIGPIPE by default.
 599         </para>
 600       </listitem>
 601       <listitem>
 602         <para>
 603           The garbage collector can now use multiple threads in parallel.
 604           The new <literal>-g<replaceable>n</replaceable></literal> RTS
 605           flag controls it, e.g. run your program with
 606           <literal>+RTS -g2 -RTS</literal> to use 2 threads.
 607           Don't use more threads than you have CPUs.
 608           Only major GCs are parallelised; minor GCs are still sequential.
 609         </para>
 610       </listitem>
 611       <listitem>
 612         <para>
 613           The <literal>-S</literal> and <literal>-s</literal> RTS flags
 614           now send their output to stderr, rather than
 615           <literal><replaceable>prog</replaceable>.stat</literal>,
 616           by default.
 617         </para>
 618       </listitem>
 619       <listitem>
 620         <para>
 621           The new <literal>-vg</literal> RTS flag provides some RTS trace
 622           messages even in the non-debug RTS variants.
 623         </para>
 624       </listitem>
 625     </itemizedlist>
 626   </sect2>
 627
 628   <sect2>
 629     <title>runghc</title>
 630
 631     <itemizedlist>
 632       <listitem>
 633         <para>
 634           runghc now uses the compiler that it came with to run the
 635           code, rather than the first compiler that it finds on the
 636           PATH.
 637         </para>
 638       </listitem>
 639       <listitem>
 640         <para>
 641           If the program to run does not have a <literal>.lhs</literal>
 642           extension then runghc now treats it as a <literal>.hs</literal>
 643           file. In particular, this means that programs without an
 644           extension now work.
 645         </para>
 646       </listitem>
 647       <listitem>
 648         <para>
 649           <literal>runghc foo</literal> will now work if
 650           <literal>foo.hs</literal> or <literal>foo.lhs</literal> exists.
 651         </para>
 652       </listitem>
 653       <listitem>
 654         <para>
 655           runghc can now take the code to run from stdin.
 656         </para>
 657       </listitem>
 658     </itemizedlist>
 659   </sect2>
 660
 661   <sect2>
 662     <title>ghc-pkg</title>
 663
 664     <itemizedlist>
 665       <listitem>
 666         <para>
 667           ghc-pkg now has a <literal>-no-user-package-conf</literal>
 668           flag which instructs it to ignore the user's personal
 669           package.conf.
 670         </para>
 671       </listitem>
 672       <listitem>
 673         <para>
 674           ghc-pkg no longer allows you to register two packages that
 675           differ in case only.
 676         </para>
 677       </listitem>
 678       <listitem>
 679         <para>
 680           ghc-pkg no longer allows you to register packages which have
 681           unversioned dependencies.
 682         </para>
 683       </listitem>
 684       <listitem>
 685         <para>
 686           There is a new command <literal>dump</literal> which is
 687           similar to <literal>describe '*'</literal>, but in a format
 688           that is designed to be parsable by other tools.
 689         </para>
 690       </listitem>
 691     </itemizedlist>
 692   </sect2>
 693
 694   <sect2>
 695     <title>Haddock</title>
 696
 697     <itemizedlist>
 698       <listitem>
 699         <para>
 700           Haddock 2 now comes with GHC.
 701         </para>
 702       </listitem>
 703     </itemizedlist>
 704   </sect2>
 705
 706   <sect2>
 707     <title>DPH changes</title>
 708
 709     <itemizedlist>
 710       <listitem>
 711         <para>
 712           DPH is now an extralib.
 713         </para>
 714       </listitem>
 715       <listitem>
 716         <para>
 717           There is a new flag <literal>-Odph</literal> that sets the
 718           flags recommended when using DPH. Currently it is equivalent
 719           to
 720           <literal>
 721             -O2 -fno-method-sharing -fdicts-cheap
 722             -fmax-simplifier-iterations20 -fno-spec-constr-threshold
 723           </literal>
 724         </para>
 725       </listitem>
 726       <listitem>
 727         <para>
 728           There are now flags <literal>-fdph-seq</literal> and
 729           <literal>-fdph-par</literal> for selecting which DPH backend
 730           to use.
 731         </para>
 732       </listitem>
 733       <listitem>
 734         <para>
 735           The <literal>-fflatten</literal> flag has been removed. It
 736           never worked and has now been superceded by vectorisation.
 737         </para>
 738       </listitem>
 739     </itemizedlist>
 740   </sect2>
 741
 742 </sect1>
 743